But he assumes that the explanandum is a fact or basic generality about biological mechanisms (rather than a genuine law or a whole theory), such as the mechanism of action potentials in neurotransmission.

Whereas in event-explanations the relation between the explanans and the explanandum is empirical, in action-explanations the relationship between the explanans and the explanandum is a logical or conceptual relation.

A theory should be formalized as a first-order deductive system with primitive terms and defined terms; some of its terms should have criteria of application to observable outcomes; explanation proceeds by deriving a description of the explanandum from the theory; and the theory should be tested by evaluating the truth or falsity of its observational consequences.